Intermittency of gravity wave momentum flux in the mesopause region observed with an all‐sky airglow imager

Abstract

The intermittency of gravity wave momentum flux (MF) near the OH airglow layer (∼87 km) in the mesopause region is investigated for the first time using observation of all‐sky airglow imager over Maui, Hawaii (20.7°N, 156.3°W), and Cerro Pachón, Chile (30.3°S, 70.7°W). At both sites, the probability density function (pdf) of gravity wave MF shows two distinct distributions depending on the magnitude of the MF. For MF smaller (larger) than ∼16 m2 s−2 (0.091 mPa), the pdf follows a lognormal (power law) distribution. The intermittency represented by the Bernoulli proxy and the percentile ratio shows that gravity waves have higher intermittency at Maui than at Cerro Pachón, suggesting more intermittent background variation above Maui. It is found that most of the MF is contributed by waves that occur very infrequently. But waves that individually contribute little MF are also important because of their higher occurrence frequencies. The peak contribution is from waves with MF around ∼2.2 m2 s−2 at Cerro Pachón and ∼5.5 m2 s−2 at Maui. Seasonal variations of the pdf and intermittency imply that the background atmosphere has larger influence on the observed intermittency in the mesopause region.

Regional Distribution of Mesospheric Small‐Scale Gravity Waves During DEEPWAVE

“…The largest values (( I ′/ I 0 ) 2 > 2, ~100 times the minimum measurements) are relatively rare (~6%), even though they are associated with waves transporting very large amounts of momentum flux, which is proportional to ( I ′/ I 0 ) 2 . Similar results have been found by Cao and Liu () who have analyzed OH airglow data obtained from Maui, HI (20.7°N) and Cerro Pachon, Chile (30.3°S).…”

“…Similar results have been found worldwide using global satellite data (Wright et al, ). More recently, Cao and Liu () have analyzed airglow images from two very distinct locations: an isolated ocean site, Maui, HI (20.7°N), and Cerro Pachon (30.3°S), in the Chilean Andes Mountains. They found that, at mesospheric altitude, intermittency is larger over the ocean site, in contrast with stratospheric observations.…”

Gravity wave momentum flux in the mesosphere measured by VHF radar at Davis, Antarctica

“…As already noted, the direct comparison of quantitative measures of intermittency derived from different observation techniques must be carefully considered in relation to sampling differences. This will be discussed in more depth in section 4; however, it is noted here that the value of I g observed in the present study for the absolute momentum flux is significantly larger than lower altitude observations in nearby regions where orographic waves are absent [ Plougonven et al , ; Jewtoukoff et al , ], similar to the mesospheric observations reported in Cao and Liu []. The higher intermittency in the zonal and meridional components as characterized by the percentage of the momentum flux above the 90th and 99th percentiles is reflected as a significant increase in the Gini coefficients above that of the absolute.…”

“…Recent observational studies using a variety of remote sensing and in situ measurements have established that the probability density functions (pdfs) of middle atmosphere gravity wave momentum flux generally exhibit a characteristic lognormal distribution [ Alexander et al , ; Hertzog et al , ; Wright et al , ; Ern et al , ; Cao and Liu , ]. The pdf analysis summarizes one of the most important characteristics of gravity waves in the middle atmosphere, previously observed on a less consistent basis [ Alexander et al , , ], that relatively small numbers of large amplitude gravity waves contribute a significant part of the total momentum flux of the gravity wave spectrum.…”

Improvement of stratospheric balloon GPS positioning and the impact on gravity wave parameter estimation for the Concordiasi campaign in Antarctica

“…This packet‐like description implicitly stresses that gravity wave activity in the atmosphere is intermittent [ Alexander et al ., ; Hertzog et al ., ; Wright et al ., ]. Several recent studies further describe observations of the intermittent nature of gravity waves [ Wright et al ., ; Cao and Liu , ; John and Kumar , ], which motivates us to use a wavelet analysis method to retrieve GW parameters.…”